This invention relates to a light beam scanning apparatus. A scanning method of scanning planes by a light beam has been recently developed for practical use, related to various reading equipment and printers, or equivalent. In response thereto, various proposals have been been made for the light beam scanning apparatus itself. For instance, an apparatus in which a laser beam is periodically deflected by a revolving polyhedral mirror is a typical example of apparatus of this kind.
One of the improvement objects for a light beam scanning apparatus has been directed towards simplification of the structure of the apparatus. As a matter of fact, a light beam scanning apparatus improved toward this object has been proposed, which is shown in FIG. 1.
A revolving disc 2 is securely mounted on the shaft of a motor 1 so as to be capable of revolving at a constant speed. On the peripheral surface of the revolving disc 2, a plurality of point light sources 3-1, 3-2, ..., 3-i, ... are equidistantly mounted. These point light sources 3-i are arranged to sequentially emit light in accordance with the revolution at a constant speed of the revolving disc 2, and as shown in FIG. 1, when the light source 3-i emits light, its diverging light beam 4 is reflected by a concave mirror 5 with a spherical reflecting surface, into a plane that is approximately parallel to the revolving disc 2, and is converged by the concave mirror 5 toward a scan plane 6. The concave mirror 5 is located in such a manner that the converging light beam reflected by the concave mirror 5 linearly scans the scan plane, regardless of the rotary displacement of the point light source 3-i.
Furthermore, by arranging the distance between the concave mirror 5 and the scan plane 6 to be adequately long, and convergence of the converging light beam to be adequately gradual, thereby making the so-called focal depth of the converging focal point sufficiently deep, the scan plane 6 can be scanned by a beam possessing a diameter that is substantially unchanged, in the direction normal to the plane of the figure, and due to the switching of the light emitting point light sources from one to the next, one and the same linear portion of the scan plane 6 can be scanned repeatedly.
This light beam scanning apparatus is disadvantageous in that a plurality of light sources is required, which will inevitably raise the cost of the apparatus, and in that as the light sources move, wiring for the circuits to energize the light sources becomes complicated.